Field of the Invention
The present invention relates to an image-processing device and a control method thereof.
Description of the Related Art
Conventional frame rate conversion methods in which a frame frequency is increased by a factor of N (N being a natural number equal to or greater than 2) include methods wherein a one-frame image is divided (distributed) into a plurality of sub-frames. Frame rate conversion methods include methods that involve dividing an input image into a sub-frame in which a high-frequency component is pre-emphasized (pre-emphasized sub-frame, hereafter referred to as “Hi image”) and a sub-frame in which a high-frequency component is reduced or de-emphasized (de-emphasized sub-frame, hereafter referred to as “Lo image”), and alternately outputting then the sub-frames. Such a method is called a drive distribution method. This drive distribution method allows reducing the perception of motion blur that arises in visual tracking (feature of vision of a moving picture whereby a moving object within the image is tracked in the line of sight). Technologies relating to drive distribution methods are disclosed in, for instance, Japanese Patent Application Publication Nos. 2009-44460 and 2009-42481. An explanation follows next on an instance where a drive distribution method is implemented, and an instance where it is not, compared with each other.
FIG. 19A and FIG. 19B are diagrams illustrating an instance where an image identical to an inputted frame image is simply outputted in the form of two sub-frame images, through frame rate conversion in which no drive distribution method is implemented. FIG. 19A illustrates, as image data, the brightness of pixels on a given horizontal line within the image. The abscissa axis direction represents pixel position, in the horizontal direction, within the image, and the ordinate axis denotes the brightness value of each pixel. The square waveform represents the change in brightness at a given coordinate in the horizontal direction. An input frame is referred to as i frame, a subsequent input frame as i+1 frame, and an intermediate frame between the i frame and the i+1 frame is referred to as i+0.5 frame (i: natural number). Movement of the square waveform rightward in the horizontal direction indicates that motion towards the right in the horizontal direction is taking place in the image. FIG. 19B illustrates a waveform (image) that is perceived (observed) by an observer when visually tracking the image of FIG. 19A so as to match the motion of the image. The abscissa axis represents a horizontal direction coordinate in a coordinate system that conforms to the motion in visual tracking, and the ordinate axis represents brightness. The solid line represents the observed waveform, and the dashed line represents an ideal waveform, i.e. what is intended, in the image data, to be perceived by the observer. The same applies to FIG. 7 and FIG. 19A to FIG. 19F.
FIG. 19A illustrates the waveforms of three frames, namely i frame, i+0.5 frame, i+1 frame (referred to as i waveform, i+0.5 waveform and i+1 waveform), for the square waveform that is moving in the horizontal rightward direction. FIG. 19B is the waveform that is observed through visual tracking. The waveform actually perceived by human vision upon visual tracking is a combination of the i waveform and i+0.5 waveform in FIG. 19A, and constitutes a waveform such as the one denoted by the solid line in FIG. 19B. As can be seen from FIG. 19B, the waveform that is observed through visual tracking (solid line) has a brightness portion of intermediate gradation, with respect to the ideal square waveform (dashed line). This portion is observed in the form of moving image blur during visual tracking.
FIG. 19C and FIG. 19D are diagrams illustrating an instance where a Hi image and a Lo image are alternately outputted through frame rate conversion relying on a drive distribution method. FIG. 19C illustrates waveforms of a Hi image, a Lo image and a Hi image that are generated for the i frame, the i+0.5 frame and the i+1 frame, in accordance with a drive distribution method, for a square waveform that is moving in the horizontal rightward direction. The waveforms will be referred to hereafter as Hi (i) waveform, Lo (i+0.5) waveform and Hi (i+1) waveform, respectively. FIG. 19D illustrates a waveform (image) that is perceived (observed) by an observer when visually tracking the image of FIG. 19C so as to match the motion of the image.
The waveform actually perceived by human vision as a result of visual tracking is a combination of the Hi (i) waveform and the Lo (i+0.5) waveform in FIG. 19C, and constitutes a waveform such as the one denoted by the solid line in FIG. 19D. As can be seen from FIG. 19D, the portion at which brightness differs significantly from that of the ideal square waveform (dashed line), in the waveform observed through visual tracking (solid line), is small, and there are fewer pixels of intermediate gradation as compared with FIG. 19B. As a result, the image is observed with less moving image blur.